Multiwall carbon nanotubes (MWCNT) are coated with ferromagnetic nickel and cobalt by a solution method. It results in a coating on the carbon nanotube surfaces in form of Ni/CoO nanoparticles. As a result of nano-scale Ni/CoO coating, MWCNT–polystyrene composites exhibit superparamagnetism at room temperature. As 3wt.% of Ni/CoO coated MWCNT is dispersed in polystyrene matrix, a viscous liquid with solvent is developed for magnetic alignment. It is found that the Ni/CoO coated MWCNT respond to magnetic field susceptibly in the viscous liquid and arrange themselves in the direction of the applied field up to 5T. Upon drying with magnetic field on, MWCNT are found to be well aligned in the direction of the field in the polystyrene matrices, as evidenced in the SEM and TEM experiments. As a result, strong anisotropy in tensile strength has been observed in the MWCNT–polystyrene composites. Magnetic alignment mechanism, surface coating microstructure of MWCNT, and related mechanical behaviors are discussed.

The time effect of ultrasonication was investigated for dispersing carbon nanofibers (CNFs) into a polycarbonate (PC) matrix on the mechanical properties of thus-produced composites. The effects of CNF surface modification by plasma treatment and the CNF concentration in composites on their mechanical properties were also explored. The plasma coating was characterized by HRTEM and FT-IR. Furthermore, the plasma polymerization (10 w) treatment on the CNF enhanced the CNF dispersion in the polymer matrix. The mechanical properties of the CNF-PC composites varied with the dispersion time, at first increasing to a maximum value and then dropping down. After a long ultrasonic treatment (24 h), the properties increased again. At a high concentration, the CNF-PC suspension became difficult to disperse. Additionally, the possible mechanisms for these behaviors are simply proposed. (c) 2006 Wiley Periodicals, Inc.

An instrumented indentation technique was tested on three types of carbon nanotube/nanofiber-reinforced composites to investigate its applicability for measuring mechanical properties (elastic modulus and hardness). There was good agreement in the measured elastic modulus between the instrumented indentation and uniaxial tension tests for the case of a nanocomposite with a harder epoxy matrix material. In contrast, there was a considerable difference in elastic modulus between the two tests for the case of a nanocomposite with a softer polystyrene matrix material. A modified area function was then developed for the nanocomposite with the softer polystyrene matrix material, and this eliminated the difference in elastic modulus between the two test techniques. Thus, the instrumented indentation technique can be used for evaluating the mechanical properties of polymer matrix nanocomposites with an added advantage that a small sample size can be used. The instrumented indentation test was also utilized in the case of a patterned nanotube array-reinforced epoxy matrix composite. This clearly showed the modulus of the array nanocomposite improved considerably compared to that of the neat epoxy resin.

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This two-part article describes a carbon nanofiber-polymethylmethacrylate (CNF-PMMA) composite material that has electrochemical actuation properties. Part I of the study considers use of a liquid electrolyte while Part II considers a solid electrolyte. Concerning Part I, a combination of solvent casting and melt mixing were used to disperse CNF in PMMA, and thin films of the material were cast. A liquid-based electrochemical actuator was formed by placing the CNF composite film in an electrolyte solution. Electrochemical impedance spectroscopy was carried out to characterize the electrochemical properties of the PMMA-CNF actuator. The actuator was tested at voltages up to 15 V and the relationship between displacement and applied voltage was determined. Compared to previous single-wall carbon nanotube buckypaper actuators, the CNF-PMMA composite actuator is stronger and is two orders of magnitude lower in cost, but needs higher voltage to actuate. Because of the low cost of the CNF hybrid material, and the possibility for using stronger host materials, new smart structural materials that enable large components and structures to actuate may become feasible.

The mechanical properties of polycarbonate film embedded with carbon nanofibers were studied based on plasma surface modification of carbon nanofibers by the use of polystyrene. The nanofiber surfaces were modified by various processing conditions including plasma polymerization power, nanofiber concentration, and ultrasonication time. The tensile strength and Young's modulus of the carbon nanofiber-polycarbonate composites were then measured. The mechanical behavior of the composite was found to be affected by dispersion of the nanofibers. Higher plasma power resulted in improved mechanical strength. A maximum strength (10% increase) was achieved at a low concentration (1 wt.%) of nanofibers. The optimization of ultrasonication time indicated that the maximum strength occurred at different times for the composites with different concentrations of the modified carbon nanofibers.

The effect of plasma surface modification and ultrasonication time on the mechanical properties of multi-wall carbon nanofiber polycarbonate composites were investigated. The study showed that plasma polymerization treatment of multi-wall carbon nanofibers enhanced the dispersion of the nanofibers in the polymer, and hence improved the mechanical properties of the nanocomposite. The study also showed that the mechanical properties of the nanocomposite depended on the ultrasonic dispersion time. Long term dispersion damaged the surfaces of both untreated and plasma polymerized carbon nanofibers. The interface behavior and strengthening mechanisms are discussed.

Engineering applications of carbon nanofibers and nanotubes require their alignment in specific directions. Single-walled carbon nanotubes can be aligned in a magnetic field due to the presence of small amounts of catalyst elements, such as Ni and Co. However, for carbon nanofibers, their extremely low magnetic susceptibility is not sufficient for magnetically induced alignment. We present a method of solution-coating of NiO and CoO onto the surface of the carbon nanofibers. Due to the NiO- and CoO-coating, these nanofibers can be well aligned in the polymer composites under moderate magnetic field (3 T). Both transmission electron microscopy and scanning electron microscopy results show the well-aligned nanofibers in a polymer matrix. Mechanical testing shows a pronounced anisotropy in tensile strength in directions normal (12.1 MPa) and parallel (22 MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO and CoO on the nanofiber surface is discussed.

Carbon nanofibers were well aligned in polymer composite magnetically at moderate fields up to 3 T. Due to the NiO-coating, carbon nanofibers exhibited strong magnetic moments that lead to alignment. Both TEM and SEM results showed the well- aligned nano-fibers in a polymer matrix. Mechanical testing showed a pronounced anisotropy in tensile strength in directions normal (12.1MPa) and parallel (22MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO on the nano fiber surface is discussed.

Ultrathin polymer films have been deposited on both multi-wall and aligned carbon nanotubes using a plasma polymerization treatment. TEM experimental results showed that a thin film of polystyrene layer (several nanometers) was uniformly deposited on the surfaces of the nanotubes including inner wall surfaces of the multi-wall nanotubes. The coated multi-wall nanotubes were mixed in polymer solutions for studying the effects of plasma coating on dispersion. It was found that the dispersion of multi-wall carbon nanotubes in polystyrene composite was significantly improved. The deposition mechanisms and the effects of plasma treatment parameters are discussed.

Ultrathin polymer films have been deposited on both single- and multi-wall carbon nanotubes using a plasma polymerization treatment. HRTEM experiments showed that an extremely thin film of the pyrrole layer (2–7 nm) was uniformly deposited on the surfaces of the nanotubes including inner wall surfaces of the multi-wall nanotubes. Time-of-Flight Secondary ion mass spectroscopy (TOFSIMS) experiments confirmed the nanosurface deposition of polymer thin films on the nanotubes. The deposition mechanisms and the effects of plasma treatment parameters are discussed.

Building artificial nerves for smart structures and for structural health monitoring is discussed. Structural Health Monitoring refers to using in-situ sensors to monitor the strains and strain waves and from these interpret the health of a structure in real-time. This will allow a structure to be operated at its maximum performance and efficiency while minimizing fatigue and other damage. To achieve this capability on a large structure, artificial nerves are used to mimic the biological nervous system. Two design concepts for nerve fibers are considered; piezoceramic active fibers and carbon nanotube conductive fibers. The piezoceramic fibers are self-powered and can sense acoustic emissions and dynamic strains due to damage. The carbon nanotube fibers change conductance when strained and can sense high strain due to damage. The processes being developed to fabricate the two types of nerves are discussed and some initial experimental results are presented.

To study interfacial particle-to-particle bonding mechanisms, an ultrathin film of pyrrole was deposited on alumina nanoparticles using a plasma polymerization treatment. High resolution transmission electron microscopy experiments showed that an extremely thin film of the pyrrole layer (2 nm) was uniformly deposited on the surfaces of the nanoparticles. In particular, the particles of all sizes (10–150 nm) exhibited equally uniform ultrathin films indicating well-dispersed nanoparticles in the fluidized bed during the plasma treatment. Time-of-flight secondary ion mass spectroscopy experiments confirmed the nano-surface deposition of the pyrrole films on the nanoparticles. The pyrrole-coated nanoparticles were consolidated at a temperature range (approximately 250 °C) much lower than the conventional sintering temperature. The density of consolidated bulk alumina has reached about 95% of the theoretical density of alumina with only a few percent of polymer in the matrix. After low-temperature consolidation, the micro-hardness test was performed on the bulk samples to study the strength that was related to particle-particle adhesion. The underlying adhesion mechanism for bonding of the nanoparticles is discussed.

Acrylic acid polymer thin films were deposited on the surfaces of nanoparticles of ZnO using a plasma polymerization treatment. The average size of nanoparticles was on the order of 50 nm in irregular shapes. High-resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin film of the acrylic acid layer (15 nm) was uniformly deposited on the surfaces of the nanoparticles. The HRTEM results were confirmed by time-of-flight secondary ion mass spectroscopy. The effect of plasma power on the polyacrylic thin film was studied by Fourier transform infrared experiments. The deposition mechanisms and the effects of plasma treatment parameters are discussed.

Ultrathin acrylic acid polymer films have been deposited on the surfaces of nanoparticles of ZnO using a plasma polymerization treatment. The average size of nanoparticles is on the order of 50 nm in irregular shapes. High-resolution transmission electron microscopy (HRTEM) experiments showed that an extremely thin film of the acrylic acid layer (15 nm) was uniformly deposited on the surfaces of the nanoparticles. In particular, the particles of all sizes exhibited equally uniform ultrathin films indicating a well-dispersed nanoparticles in the fluidized bed during the plasma treatment. The deposition mechanisms and the effects of plasma treatment parameters are discussed.